This invention relates to railcar trucks and more particularly to an improved constant contact type side bearing mountable on a truck bolster to contact the underside of a railcar body.
The usual freight railcar comprises a car body supported on at least one, and usually two, wheeled trucks that are confined to roll on rails. Each truck includes a truck bolster that extends essentially transversely of the car body longitudinal center line and pivotally supports the car body. In the preponderance of freight cars in domestic use, the pivotal connection is made by center bearing plates and bowls transversely centered on the car body underframe and the truck bolster. Accordingly, the truck may turn or pivot on the center plate under the car body and, under certain dynamic conditions and car speeds during operation, the truck may tend to adversely oscillate or "hunt" in a yaw-like manner beneath the car body. Also, the car body is subject to adversely roll from side to side during operation. Side bearings positioned on the truck bolster outwardly of the center bowl are commonly employed to control both such adverse conditions by frictionally retarding oscillations and cushioning and limiting the extent of the rolling motions. Constant contact type side bearings usually include a base that is fastened to the bolster and a cap that is biased upward from the base so as to contact bearing pads on the car body underframe. The cap must be free to move vertically with respect to the base, and during the course of operation, the clearance between those parts will be enlarged due to abrasion and wear. Pivotal movement of the truck beneath a car body will apply large frictional forces to the cap in a generally longitudinal direction of the car body tending to wear the longitudinal ends of the cap and base. As longitudinal wear occurs the cap becomes free to move longitudinally and thus, the ability to dampen oscillations (hunting) of the truck is reduced. Also, the longitudinal forces tend to cant or tilt the cap with respect to the base and that tendency increases as the clearance between cap and base becomes enlarged through wear. When the cap becomes canted, the ability to dampen oscillations (hunting) and cushion roll will be further hindered.